MTN is ******** about Cellphone contact end dates

I opened a cellphone contract for my daughter two years ago for a duration of two years. The contract came to an end in August 2023. Because I was in a similar position with another cellphone service provider a couple of years ago i made sure to send them an email well in advance telling them of my intention to terminate all services connected to the phone once the contract expire. This means I don't want any extensions of any plans on the phone because it's paid up and my daughter will revert to prepaid. Mtn received my email of cancellation but still went ahead and billed me for September and I also see the bill for October just arrived via email. They just turn a blind eye to my emails and keep on sending me invoices. The contract in question is Account BA***